Null for QDateEdit

[wirasto]

if I use QDateEdit, automaticaly I have a date value. Well, how to set "null" value for QDateEdit like setCurrentIndex(-1) in QComboBox ?
I tried reimplement QDateEdit widget and set like this. But failed

myDE::myDE(QWidget *parent)
        :QDateEdit(parent)
{
    setCalendarPopup(true);
    calendarWidget()->setGridVisible(true);
    setDate(QDate::currentDate());
    setMaximumDate(QDate::currentDate());
 
    QLineEdit *le=new QLineEdit();
    setLineEdit(le);
    le->clear();
}

myDE::myDE(QWidget *parent)
        :QDateEdit(parent)
{
    setCalendarPopup(true);
    calendarWidget()->setGridVisible(true);
    setDate(QDate::currentDate());
    setMaximumDate(QDate::currentDate());

    QLineEdit *le=new QLineEdit();
    setLineEdit(le);
    le->clear();
}

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